As conventional materials of contact and terminal parts, such as connectors and switches, there are used plated products wherein a base material of stainless steel, copper, a copper alloy or the like, which is relatively inexpensive and which has excellent corrosion resistance, mechanical characteristics and so forth, is plated with tin, silver, gold or the like in accordance with required characteristics, such as electrical and soldering characteristics.
Tin-plated products obtained by plating a base material of stainless steel, copper, a copper alloy or the like, with tin are inexpensive, but they do not have good corrosion resistance. Gold-plated products obtained by plating such a base material with gold have excellent corrosion resistance and high responsibility, but the costs thereof are high. On the other hand, silver-plated products obtained by plating such a base material with silver are inexpensive in comparison with gold-plated products and have excellent corrosion resistance in comparison with tin-plated products.
As such a silver-plated product, there is proposed a metal plate for electrical contacts, wherein a silver plating film having a thickness of 1 micrometer is formed on a copper plating film having a thickness of 0.1 to 0.5 micrometers which is formed on a nickel plating film having a thickness of 0.1 to 0.3 micrometers which is formed on the surface of a thin base material plate of stainless steel (see, e.g., Japanese Patent No. 3889718). There is also proposed a silver-coated stainless bar for movable contacts, wherein a surface layer of silver or a silver alloy having a thickness of 0.5 to 2.0 micrometers is formed on an intermediate layer of at least one of nickel, a nickel alloy, copper and a copper alloy having a thickness of 0.05 to 0.2 micrometers, the intermediate layer being formed on an activated underlying layer of nickel which has a thickness of 0.01 to 0.1 micrometers and which is formed on a base material of stainless steel (see, e.g., Japanese Patent No. 4279285). Moreover, there is proposed a silver-coated material for movable contact parts, wherein a surface layer of silver or a silver alloy having a thickness of 0.2 to 1.5 micrometers is formed on an intermediate layer of copper or a copper alloy having a thickness of 0.01 to 0.2 micrometers, the intermediate layer being formed on an underlying layer of any one of nickel, a nickel alloy, cobalt or a cobalt alloy which has a thickness of 0.005 to 0.1 micrometers and which is formed on a metallic substrate of copper, a copper alloy, iron or an iron alloy, the arithmetic average roughness Ra of the metallic substrate being 0.001 to 0.2 micrometers, and the arithmetic average roughness Ra after forming the intermediate layer being 0.001 to 0.1 micrometers (see, e.g., Japanese patent Laid-Open No. 2010-146925).
However, if such a conventional silver-plated product is used as the material of automotive sliding switches and so forth, there is some possibility that the silver plating film thereof may be worn due to repeated sliding movements to expose the base material thereof to increase the electrical resistance thereof, so that the wear resistance thereof against the sliding movements is not sufficient.